The present invention relates to a method and apparatus for winding a continuously advancing yarn into a yarn package, wherein the package is formed on a driven winding spindle be mounted in cantilever fashion on a moveable support such as a rotatable turret, and wherein a moveable contact roll rests on the surface of the package being formed.
During such winding processes, the increase in the diameter of the package as the package builds is accommodated by an evading movement of the package or the contact roll. Also, the contact force between the package and the contact roll is predetermined by a hydraulic or pneumatic biasing force. Since the center distance between the contact roll lying against the circumference of the package and the package likewise affects the contact force, the change of the center distance causes the contact force to change at the same time. This gives rise to the problem that on the one hand a predetermined contact force is always present between the contact roll and the package and that on the other hand, however, the package diameter is allowed to increase unimpeded.
EP 0 374 536 and corresponding U.S. Pat. No. 5,029,762 disclose a method and a winding or takeup machine, wherein the evading movement of the winding spindle receiving the package during a winding cycle is controlled as a function of the position of the contact roll. In this instance, the evading movement of the winding spindle may occur in steps or continuously. Since the contact force between the contact roll and the package depends on the relative position between the contact roll and the package, it is not possible to avoid a change of the contact force during the winding cycle.
U.S. Pat. No. 5,407,143 discloses a takeup machine, wherein the rotational movement of a spindle turret with a winding spindle projecting therefrom is controlled in such a manner that the contact force between a contact roll and the package maintains a predetermined desired value. In this instance, an adjusting device for changing the center distance is simultaneously used for controlling the contact force. This produces unwanted changes of the contact force due to stick-slip effects.
WO 96/01222 discloses a method and a takeup machine, wherein the rotational movement of the spindle turret occurs as a function of the angular position of the winding spindle. From the correlation between the angular position of the winding spindle on the spindle turret and the diameter of the package, one may conclude the associated angular position from the changing diameter. Since the contact roll resting against the package is stationary, the increase of the package causes an increase of the contact force between the contact roll and the package. In addition, the method may lead--in particular in the case of soft packages--to an overtraveling of the spindle turret, so that the contact between the contact roll and the package is totally lost.
Likewise, the method disclosed in DE 195 38 480 has the disadvantage that the stepwise rotational movement of the spindle turret as a function of the angular position of the winding spindle causes in the course of the winding cycle a discontinuous change of the contact force between the package and the contact roll, which is caused by the increase of the package diameter. In the known method, a time is predetermined, after which the angular velocity of the spindle turret is periodically computed as a function of the position of the spindle turret. Since the chronological diameter increase of the package requires a substantially faster change of the angular velocity of the spindle turret at a small package diameter in comparison with a large package diameter, fluctuations in the contact force are incurred at the beginning of the winding cycle.
It therefore an object of the invention to further develop a method of winding a continuously advancing yarn as initially described as well as a takeup machine for carrying out the method such that the yarn is wound on the package during the entire winding cycle with a predetermined contact force or a predetermined contact force profile at a substantially constant speed of advance of the yarn.